5/16-18 Phillips Flat Head Zinc

PHILLIPS FLAT HEAD, STEEL, ZINC, MACHINE SCREWS. Aside from material, machine screws differ in head shape, head type, diameter, length, threading and purpose. Machine screws are designed to hold two pieces of material together. Most machine screws require the hole already be drilled and threaded, although there are a few machine screws capable of tapping their own hole. (Search for Thread Cutting Screws).